Recently, water pollution with nitrate nitrogen is becoming serious social concern year by year together with ground water contamination with organochlorine compounds such as trichloroethylene. Nitrate nitrogen which are contaminants of said ground water and also derive from nitrogen fertilizers and pesticides also exist as nitrates and nitrites in organisms.
That is, organic nitrogen contained in debris will penetrate into soil, become decomposed into ammonia nitrogen therein and subsequently oxidized to nitrate through nitrite.
Therefore, nitrate nitrogen is widely distributing in many plants, particularly in vegetables since nitrate nitrogen in ground water, although mainly exist as nitrates in ground water, after easily translocated together with ground water, or nitrate nitrogen derived from fertilizers or pesticides again are taken up by plants and incorporated into organisms.
Toxicity of said nitrates to human is believed due to reduction of nitrate by microorganisms in the body to nitrites. It is well known that said nitrites not only oxidizes hemoglobin having an important rule as an oxygen transporter in blood to methemoglobin which lacks the oxygen transport ability, resulting in oxygen deficiency in various organs, but also causes adverse effect such as senescence of blood vessels. Further, it is known that nitrites reacts in stomach with secondary amines, non-carcinogens, to form nitrosoamines, carcinogens.
As ordinary methods to obtain powdered vegetable juice or powdered vegetables as food supplements, several methods are proposed; a method to freeze-dry fresh vegetables followed by pulverization using a mill, a method to dry fresh vegetables using a dryer followed by pulverization using a mill, another method to squeeze fresh vegetables avoiding decomposition of components, freeze-drying the resulting liquid followed by further pulverization using a mill. But, there are no methods referring nitrate nitrogen harmful to human body, contained in or deposited on vegetables.